It is known that a packet communication method is provided in which a link is identified from an address field of a packet, an information frame is transmitted and received as confirmation information, and a packet length has statistical deviation (for example, refer to Japanese Laid-open Patent Publication No. 1-146445). A packet communication system by the above-described method is provided with a buffer pool including a plurality of kinds of buffers in accordance with packet lengths, and a data receiver that distributes received packets into the individual buffers of the buffer pool in accordance with the packet length. In the packet communication system, the number of buffers is increased for a packet to be transmitted and received with priority. Also, in the packet communication system, if there is no buffer capable of receiving data at packet reception time, a link is identified from the address field, and notifies that the station is busy only to that link. Also, the packet communication system is provided with a function of notifying that the station is busy to all the links if the total number of empty buffers exceeds a predetermined number, and a flow controller having a function of setting the station ready if the total number of empty buffers exceeds a certain fixed number.
Also, it is known that a packet communication network connection apparatus is provided that mutually connects networks communicating by variable-length packets (for example, refer to Japanese Laid-open Patent Publication No. 10-271163). A determination unit determines a received packet to be a short packet if the packet length is a predetermined value or less, and if not, determination unit determines the received packet to be a long packet. A priority transmission unit transmits short packets with priority over long packets.
Also, a priority control method using a single output queue is known (for example, refer to Japanese Laid-open Patent Publication No. 2001-177575). In the priority control method, the output priority of packets without congestion is improved by exchanging packet orders between packets with congestion or packets that might be congested, and packets without congestion.
A packet length of an access request to a memory is different depending on a type of the access request, and is not fixed. On the other hand, a memory has a limitation as a resource for reception processing, and thus it often happens that an access request is difficult to be processed all the time. In this case, an access request to the memory is processed after waiting for a moment when the resources become free. The remaining number of the memory resources becomes insufficient, and thus transmission of an access request is kept waiting. Accordingly, the throughput of the arithmetic processing unit deteriorates.